Migrations即迁移，它是EF的code first模式出现的产物，它意思是说，将代码的变化反映到数据库上，这种反映有两种环境，一是本地开发环境，别一种是服务器的生产环境，本地开发环境主要使用包管理工具的update-database即可完成数据库的迁移（变更），而在生产环境就显得麻烦一些，因为你不会在生产环境放程序源代码和ＶＳ开发工具，哈哈．

本地数据库迁移请看我的这篇文章

服务器上生产环境的数据迁移

如果我们有迁移文件如下

public partial class manager : DbMigration    {
            /// 
         /// 要在升级过程中执行的操作。         /// 
        public override void Up()        {            DropForeignKey("dbo.WebDataSettings", "WebDataCtrlId", "dbo.WebDataCtrls");            DropForeignKey("dbo.WebDataSettings", "DepartmentId", "dbo.WebDepartments");            RenameColumn(table: "dbo.WebDataSettings", name: "DepartmentId", newName: "WebDepartmentsId");            RenameIndex(table: "dbo.WebDataSettings", name: "IX_DepartmentId", newName: "IX_WebDepartmentsId");            AddForeignKey("dbo.WebDataSettings", "WebDataCtrlId", "dbo.WebDataCtrls", "ID", cascadeDelete: true);            AddForeignKey("dbo.WebDataSettings", "WebDepartmentsId", "dbo.WebDepartments", "ID", cascadeDelete: true);        }   /// 
         /// 要在降级过程中执行的操作。         /// 
        public override void Down()        {            DropForeignKey("dbo.WebDataSettings", "WebDepartmentsId", "dbo.WebDepartments");            DropForeignKey("dbo.WebDataSettings", "WebDataCtrlId", "dbo.WebDataCtrls");            RenameIndex(table: "dbo.WebDataSettings", name: "IX_WebDepartmentsId", newName: "IX_DepartmentId");            RenameColumn(table: "dbo.WebDataSettings", name: "WebDepartmentsId", newName: "DepartmentId");            AddForeignKey("dbo.WebDataSettings", "DepartmentId", "dbo.WebDepartments", "ID");            AddForeignKey("dbo.WebDataSettings", "WebDataCtrlId", "dbo.WebDataCtrls", "ID");        }    }

在本地ＶＳ中执行下面命令，它将生产迁移计划，即ＳＱＬ语句

Update-Database -Script -SourceMigration: $InitialDatabase -TargetMigration:manage

它将生成对应的ＳＱＬ脚本，我们在服务器上运行即可

幂等性

由Migration生成的ＳＱＬ脚本是幂等的，即，当你多次执行ＳＱＬ脚本时，产生的结果是一样的，不对有负作用．